The invention relates to an electrophotographic recording material for preparing a printing form or a printed circuit comprising a layer support and a photoconductive layer composed of photoconductor, sensitizer and/or activator, if appropriate further additives which improve surface texture and/or adhesion, and a high molecular weight binder which is soluble in an alkaline-aqueous or alcoholic solution.
It is known to use photoconductive layers of monomeric or polymeric organic photoconductors, sensitizers and/or activators and alkali-soluble binders on appropriate supports to prepare printing forms or printed circuits by electrophotographic means (German Pat. No. 1,117,391, which is equivalent to British Pat. No. 944,126). The photoconductive layers are applied to a suitable metallic or metallized support by suitable coating techniques from solution or by laminating, as disclosed in German Offenlegungsschrift No. 3,024,772. The high molecular weight binder contains alkali-solubilizing groups such as acid anhydride, carboxyl, phenol, sulfonic acid, sulfonamide or sulfonimide groups (German Pat. No. 2,322,047, equivalent to U.S. Pat. No. 4,066,453). Copolymers of styrene and maleic anhydride, phenolic resins or copolymers of styrene, methacrylic or acrylic acid and methacrylates are specifically mentioned for use as binders.
To prepare a printing form or a printed circuit, the electrophotographic recording material is electrostatically charged, exposed or imagewise electrostatically charged, and developed with a toner of a dry or liquid developer. The resulting toner image can be fixed by heating to 100.degree. up to 250.degree. C., and the layer is then decoated by treating it with an alkaline-aqueous or alcoholic solution, the treatment dissolving away those areas which are not covered by the toner. The final product is a planographic printing form or a mask for a printed circuit.
Film-forming acidic polymers are also known (U.S. Pat. No. 3,422,075) which are obtained by reacting a hydroxyl- or amino-containing polymer with a monosulfonyl isocyanate. They are soluble in alkali, and can be used as a film or sheet or as a coating material, in particular in place of resinous compounds containing carboxyl groups. Their use in the preparation of photographic layers is known.
It is also known (German Auslegeschrift No. 2,053,363, equivalent to U.S. Pat. No. 3,732,106) to use in mixtures for photopolymer layers a reaction product of a sulfonyl isocyanate and a vinyl alcohol polymer, epoxy resin having free OH groups, partial cellulose esters or ethers, polyamides or copolymers of these materials. The mixture can be used in the form of a solution or dispersion as a photoresist, which is applied to an individual support and exposed and developed after drying, for preparing printed circuits or it can be used in the form of a solid layer on a support as a light-sensitive material for preparing printing forms, in particular planographic printing plates.
A proposal also has been made for a light-curable mixture (German Offenlegungsschrift No. 3,036,077) which contains as the light-sensitive compound a diazonium salt polycondensation product or an organic azido compound, and as binder a high molecular weight polymer which has lateral sulfonylurethane groups and is soluble or at least swellable in aqueous-alkaline solutions, the polymer having lateral alkenylsulfonyl urethane or cycloalkenylsulfonyl urethane groups.
The disadvantage in preparing a printed circuit by electrophotographic means using known methods is that the layers containing the alkali-solubilizing binder can be applied or laminated to a copper-clad circuit board either not at all or only at relatively high temperatures. The high temperatures hinder the laminating process, and tend to damage the, usually, thermosensitive photoconductive substances, sensitizers and activators. As a result, the photoconductive layer loses some of its photosensitivity. A further disadvantage is that the layers which contain the known alkali-soluble binders and which are used for the electrophotographic process are no longer sufficiently flexible when about 30 .mu.m thick, which thickness is required for the manufacture of printed circuit boards. It is therefore necessary to handle these layers with extreme care, because even slight bending causes undesirable cracking, thereby rendering the layer unusable.
To prepare a form or a printed circuit by electrophotographic means, solvents must be added to the decoating solution to increase the rate of the process. After use, these solvent-containing decoating solutions pass into the effluent, where they are responsible for substantial pollution of the environment.
A further disadvantage of the known alkali-soluble binders is the impairment of electrophotographic sensitivity, in particular when the layers are thick.